1. Field of the Invention
The present invention relates to a toner and two-component developer to be used in an electrophotographic system, an electrostatic recording system, an electrostatic printing system, or a toner jet system.
2. Description of the Related Art
In association with the widespread use of a copying machine and a printer, performance required for toner has become more and more sophisticated, and hence additionally high image quality and additionally high endurance stability have been required. Further, the copying machine and the printer that have heretofore been used mainly in an office have started to be used in a severe environment such as a high-temperature and high-humidity environment. It has become important to provide stable image quality even in such case.
The density of a toner for a copying machine and printer to be used in two-component development on a photosensitive member may vary owing to a change in charge quantity of the toner due to its friction with a carrier. In that case, a detrimental effect on its density stability or the like occurs. Particularly under a high-temperature and high-humidity environment, the charge quantity is liable to reduce owing to the friction with the carrier and a reduction in charge quantity of the toner due to its endurance is liable to be a problem. In order that image quality may be maintained even in use under the high-temperature and high-humidity environment, a toner whose triboelectric charge quantity does not change even after its endurance, i.e., a toner having high environmental stability and high endurance stability has been required.
In order that the toner having high environmental stability and high endurance stability may be achieved, studies have been made on the kind of an external additive and the control of the presence state of an external additive for increasing the triboelectric charge quantity of the toner on a toner surface.
Japanese Patent Application Laid-Open No. 2012-133338 proposes an approach involving fixing an inorganic fine particle to the surface of a toner particle through toner surface treatment with hot air. An improvement in stability of a charge quantity against friction with a magnetic carrier has been achieved by suppressing the desorption of the inorganic fine particle.
Japanese Patent No. 4944980 proposes a toner obtained by adding inorganic fine powder having a specific perovskite crystal. The toner has achieved an improvement in image quality by alleviating image deletion at the time of image formation under a high temperature and a high humidity, but has not sufficiently suppressed a fluctuation in image density due to a reduction in charge quantity.
When the toner described in Japanese Patent Application Laid-Open No. 2012-133338 or Japanese Patent No. 4944980 is used in a copying machine or a printer under a severe environment such as a high-temperature and high-humidity environment, the toner has been unable to satisfy the required performance. It cannot be said that its charging stability and density stability are sufficiently satisfactory, and hence an additional improvement has been required.